Setback-responsive igniter for ordnance projectiles



C. FYFE Feb. 4, 19%

SETBACK-RESPONSIVE IGNITER FOR ORDNANCE PROJECTILES Filed Dec. 21, 1954 INVENTOR C/ayfan F yfe ATTORNEYS United States Patent 2 Claims This invention relates to ordnance projectiles and more particularly to means for causing ignition in response to predetermined setback. The invention is especially adapted to the ignition of thermal batteries used in ordnance fuzes.

Thermal batteries provide a convenient source of electrical power for electronic fuzes in ordnance projectiles. These batteries are constructed with electrolytes that are inactive at normal temperatures; when power is desired, the battery is activated by heating to a suitable tempera ture. Typically, thermal batteries for ordnance devices are heated by means of a combustible mass of pyrotechnic powder in which the battery is embedded; to activate the thermal battery and thus the fuze, the powder must be ignited. The ignition should preferably be accomplished automatically with firing of the projectile. Past methods of causing ignition have included electric igniters requiring outside power, and mechanical percussion ignite'rs requiring elaborate mechanical triggering mechanisms.

A suitable ignition means must be immune to accidental ignition, prior to firing of the projectile, as a result of dropping or rough handling; such accidental ignition would, if nothing worse, render the fuze inoperative for want of power after firing of the projectile.

A principal object of the present invention is to provide a simple, economical, rugged, and reliable device for igniting the combustible heating material associated with a thermal battery in an electronic ordnance fuze, said device to be responsive only to accelerations of the magnitudes and durations to which ordnance projectiles are subjected on firing.

In my invention, predetermined setback forces encoun tered upon firing of the projectile carrying the igniter cause release of a lock mechanism, permitting a first body to move rearward and to strike a second body. These bodies are of compositions resembling those used for the heads of well-known ignitible matches and for the surfaces commonly provided for striking such matches. When the first body strikes the second body in my invention, one or both of the bodies become ignited and in turn ignite pyrotechnic powder or other combustible material. A setback-responsive lock having certain features similar to that utilized in my invention is described in US. Patent 2,625,881 to J. Rabinow.

Other objects, aspects, uses, and advantages of the invention will become apparent from the following description and from the accompanying drawing, in which:

FIGURE 1 is a longitudinal section of an igniter in accordance with the invention, embedded in a mass of combustible material. The igniter elements are shown in their initial positions, prior to setback.

FIGURE 2 is a longitudinal section of the igniter of FIG. 1 at a later time, just after setback forces have caused the lock mechanism to become released.

FIGURE 3 is a longitudinal section of the igniter of FIG. 1 at a still later time, when ignition is occurring.

In FIG. 1, igniter 9 is shown embedded in a mass of combustible material 10. Igniter 2 comprises an outer cylindrical shell 11 having a pair of opposed recesses 12a and 12b near its forward end and apertures 15a and 15b 3,425,351 Patented Feb. 4, 1969 for flame progagation near its rearward end. Shell 11 is closed at both ends by closing plates 13a and 13b. A cylindrical striker body 16 having an axial cavity 17 and opposed apertures 18a and 18b alignable with recesses 12a and 12b fits slidably inside shell 11. Balls 21a and 21b protrude through apertures 18a and 18b respectively. for flame propagation near its rearward end. Shell 11 into recesses 12a and 12b respectively.

As long as balls 21a and 21b remain in this position, they prevent striker body 16 from moving rearward within shell 11. Setback pin 23 is interposed between balls 21a and 21b and, as long as it remains in this position, prevents them from moving inward and freeing striker body 16.

A rear projection 27 of striker body 16 has a coating 28 of a material adapted to cause ignition of an ignitible body 31 upon friction therewith. Compositions similar to those used for providing striking surfaces on the sides of boxes of well-known varieties of matches are suitable. I prefer to use a coating of powdered stable red phosphorus with a shellac binder.

Ignitible body 31, adapted to ignite when struck by coating 28, is mounted at the rear end of shell 11. Body 31 may be of a composition similar to those commonly used for the heads of ignitible matches of well-known types. I prefer to use a composition of 88 percent potassium chlorate, 10 percent powdered willow charcoal, and 2 percent dextrin (by Weight).

It will be understood that the shape of body 31 is not particularly critical, but that it should preferably present a relatively large grazing surface to coating 28 when coating 28 moves rearward. I prefer that body 31 be generally cup-shaped, with a tapered, or conical, inner surface, as shown in the drawing.

Referring to FIG. 2, when firing of the projectile in which the igniter is carried has caused a sufficient setback force to act on setback pin 23 for a sufiicient period of time, setback pin 23 moves a sufficient distance rearward, against the opposing force of helical spring 24, to permit balls 18:: and 18b to move inward. It will be understood that, with continued setback, striker body 16 will be urged rearward and that the rearward force of striker body 16 on balls 21a and 21b will urge balls 21a and 21b inward. Striker body 16 thus becomes free to move rearward on continued setback, overcoming the opposing force of helical spring 25.

If rough handling should cause striker body 16 to become prematurely unlocked, spring 24 prevents accidental ignition and urges body 16 back into the locked position.

Referring to FIG. 3, with continued setback striker body 16 has now moved rearward causing friction coating 28 to strike against ignitible body 31, thereby igniting the latter. Apertures 15a and 15b permit the spread of flame from ignitible body 31 to combustible material 10 which thus becomes ignited,

It will be apparent that the embodiments shown are only exemplary and that various modifications can be made in construction and arrangement within the scope of the invention as defined in the appended claims.

I claim:

1. In a thermal battery having a mass of combustible material, an igniter responsive to acceleration forces, said igniter comprising: a cylindrical shell inserted in said material, the inner surface of said shell having two opposed recesses near its forward end, said shell having a plurality of flame-propagation openings near its rearward end; a hollow cylindrical striker body having two opposed apertures alignable with said two recesses, said striker body being slidable axially in said shell; two balls protruding axially into said apertures and recesses thereby preventing sliding of said striker body; a setback pin interposed between said balls and preventing inward motion of said balls, said setback pin being axially slidable within said striker body; first spring means within said striker body biasing said setback pin axially in the forward direction; second spring means biasing said striker body axially in the forward direction; a friction body on the rearward end of said striker body; and a frictionignitible body at the rearward end of said shell; the aboveidentified elements being so constructed and arranged that said setback pin moves rearward on predetermined setback thereby permitting said balls to move inward and permitting said striker body to move rearward on continued setback thereby causing said friction body to strike and ignite said ignitible body, flame from said ignitible body thereupon propagating through said openings to said mass of combustible material.

2. The invention according to claim 1, said frictionignitible body having a conical inner surface, said surface being coaxial with said striker.

References Cited UNITED STATES PATENTS 708,411 9/1902 Semple 108-70 2,130,115 9/1938 Biddle 52-251 2,589,607 3/1952 Ellern 5228 2,625,881 1/1953 'Rabinow 102-78 FOREIGN PATENTS 109,858 10/1917 Great Britain.

VERLIN R. PENDEGRASS, Primary Examiner. 

1. IN A THERMAL BATTERY HAVING A MASS OF COMBUSTIBLE MATERIAL, AN INTEGER RESPONSIVE TO ACCELERATION FORCES, SAID IGNITER COMPRISING: A CYLINDRICAL SHELL INSERTED IN SAID MATERIAL, THE INNER SURFACE OF SAID SHELL HAVING TWO OPPOSED RECESSES NEAR ITS FORWARD END, SAID SHELL HAVING A PLURALITY OF FLAME-PROPAGATION OPENINGS NEAR ITS REARWARD END; A HOLLOW CYLINDRICAL STRIKER BODY HAVING TWO OPPOSED APERTURES ALIGNABLE WITH SAID TWO RECESSES, SAID STRIKER BODY BEING SLIDABLE AXIALLY IN SAID SHELL; TWO BALLS PROTRUDING AXIALLY INTO SAID APERTURES AND RECESSES THEREBY PREVENTING SLIDING OF SAID STRIKER BODY; A SETBACK PIN INTERPOSED BETWEEN SAID BALLS AND PREVENTING INWARD MOTION OF SAID BALLS, SAID SETBACK PIN BEING AXIALLY SLIDABLE WITHIN SAID STRIKER BODY; FIRST SPRING MEANS WITHIN SAID STRIKER BODY BIASING SAID SETBACK PIN AXIALLY IN THE FORWARD DIRECTION; SECOND SPRING MEANS BIASING SAID STRIKER BODY AXIALLY IN THE FORWARD DIRECTION; A FRICTION BODY ON THE REARWARD END OF SAID STRIKER BODY; AND A FRICTIONIGNITIBLE BODY AT THE REARWARD END OF SAID SHELL; THE ABOVEIDENTIFIED ELEMENTS BEING SO CONSTRUCTED AND ARRANGED THAT SAID SETBACK PIN MOVES REARWARD ON PREDETERMINED SETBACK THEREBY PERMITTING SAID BALLS TO MOVE INWARD AND PERMITTING SAID STRIKER BODY TO MOVE REARWARD ON CONTINUED SETBACK THEREBY CAUSING SAID FRICTION BODY TO STRIKE AND IGNITE SAID IGNITIBLE BODY, FLAME FROM SAID IGNITIBLE BODY THEREUPON PROPAGATING THROUGH SAID OPENINGS TO SAID MASS OF COMBUSTIBLE MATERIAL. 